Force Switch

ABSTRACT

A mechanical force switch to be disposed along a longitudinal device axis of a medical device includes an electrically conductive switching piston to form a first electrical contact of the switch, a hollow body, an end stop, a bias device, and an electrically conductive second contact of the switch electrically insulated from the piston. The piston is movably disposed in the body hollow along the axis to define different switch-making and -breaking positions. The piston is also movably disposed in a cavity of the stop and the stop is disposed in the body. The stop can be a smooth or threaded puck. The bias device surrounds the piston and imparts bias against it to retain it in one of the two positions until an external axis force overcomes the bias, at which time the switch indicates a state changeover. The switch can be normally open or closed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is:

a divisional of U.S. application Ser. No. 11/750,622, filed May 18,2007;

a divisional of U.S. application Ser. No. 12/270,518 filed on Nov. 13,2008, which applications claimed the priority, under 35 U.S.C. §119, ofU.S. Provisional Patent Application 60/801,989 filed May 19, 2006,60/810,272, filed Jun. 2, 2006, 60/858,112, filed Nov. 9, 2006, and60/902,534, filed Feb. 21, 2007; and

is related to U.S. patent application Ser. Nos. 11/705,381, 11/705,334,and 11/705,246, all filed Feb. 12, 2007;

the entire disclosures of which are all hereby incorporated herein byreference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

FIELD OF THE INVENTION

The present invention lies in the field of switches, in particular, aforce switch. The device can be used along with any tool in which aparticular longitudinal force needs to be overcome prior to reaching agiven detected force.

BACKGROUND OF THE INVENTION

In various applications, a compressible material is compressed betweentwo surfaces for modification of the material in some way after beingcompressed. The material can be compressed too little, too much, or inan acceptable range of compression. It would be beneficial to provide anelectrical switch that can indicate when the acceptable minimumcompression force has been exceeded. It would further benefit if theswitch actuates over a small gap and is longitudinally in-line with thedevice in which the switch is incorporated. It would also be beneficialif the minimum force setting of the switch could be pre-set to givenforce values.

BRIEF SUMMARY OF THE INVENTION

The invention overcomes the above-noted and other deficiencies of theprior art by providing an electronic switch that actuates over a smallgap (on the order of 25 to 200 micrometers), is longitudinally in-linewith the device in which the switch is incorporated, and switchesdependent upon a longitudinally expanding external force that can bepre-set over a given floor force value.

A characteristic of the force switch described herein is that thelongitudinal forces that the force switch can withstand aresignificantly higher than that existed in the past. With a force switchhaving approximately a 6 mm diameter, for example, an approximately 5 to8 pound longitudinally pulling force changes the switch state while, atthe same time, being able to withstand almost 300 pounds of longitudinalpulling or compressive force. This is an almost twenty-fold difference.

There are many uses for the force switch in various different technologyareas.

In a first exemplary area of technology, the force switch can be used tomeasure compressive forces imparted upon tissue by medical devices. Inmany medical procedures, tissue is compressed between two surfacesbefore a medical device is caused to make a change in the compressedtissue. If the tissue is compressed too little, then the change soughtto be effected might not be sufficient. If the tissue is, on the otherhand, compressed too much, the change sought to be effected mightactually destroy the area of interest. When compressing such tissue,there are measurable force ranges that fall between these two extremes.Knowing the “safe” force range can allow the user to select apre-tensioning of the force switch to change its state (i.e., indicateto the user the pre-tensioned force has been exceeded) within the “safe”range of that tissue.

The force switch described herein can be constructed in a customized wayto have the state-changing pre-tension match the “safe” range of thetissue to be operated upon.

One type of medical device that is used to change a state of tissue is amedical stapling device. Ethicon Endo-Surgery, Inc. (a Johnson & Johnsoncompany) manufactures and sells such stapling devices. Circular staplingdevices manufactured by Ethicon are referred to under the trade namesPROXIMATE® PPH, CDH, and ILS. Linear staplers manufactured by Ethiconunder the trade names CONTOUR and PROXIMATE also can use the forceswitch. In each of these exemplary staplers, tissue is compressedbetween a staple cartridge and an anvil and, when the staples areejected, the compressed tissue is also cut. In this specific example,the tissue can be compressed too little (where blood color is stillpresent in the tissue, too much (where tissue is crushed), or just right(where the tissue is blanched). Staples delivered have a given lengthand the cartridge and anvil need to be at a given distance so that thestaples close upon firing. Therefore, these staplers have devicesindicating the relative distance between the two planes and whether ornot this distance is within the staple length firing range. However,these staplers do not have any kind of active compression indicator thatwould also optimize the force acting upon the tissue that is to bestapled. The force switch described herein provides such a feature. Someexemplary procedures in which these staplers could use the force switchinclude colon dissection and gastric bypass surgeries.

With the foregoing and other objects in view, there is provided, inaccordance with the invention, a mechanical force switch to be disposedalong a longitudinal device axis of a medical device, the switchincluding a switching piston having a longitudinal piston axis disposedparallel to the longitudinal device axis and a bias-device contact, ahollow body defining a body interior cavity in which the switchingpiston is movably disposed along the piston axis to define aswitch-making piston position at a first longitudinal piston positionwith respect to the body and a switch-breaking piston position at asecond longitudinal piston position with respect to the body differentfrom the first longitudinal piston position, a bias device imparting avariable longitudinal bias to the switching piston to retain theswitching piston in one of two positions selected from the switch-makingpiston position and the switch-breaking piston position until anexternal force imparted to the switching piston along the longitudinalpiston axis exceeds the longitudinal bias and, when the external forceexceeds the longitudinal bias, the switching piston moves to the otherof the two positions, and an electrically-conductive contact physicallycoupled to the switching piston and moveable between the two positionsto define a switch-making state, when the switching piston is in theswitch-making piston position, and a switch-breaking state, when theswitching piston is in the switch-breaking piston position.

In accordance with another feature of the invention, there is providedan end stop defining a second interior cavity in which the switchingpiston is movably disposed, the end stop being at least partly disposedin the body interior cavity.

In accordance with a further feature of the invention, the bias deviceis disposed about at least a portion of the switching piston between theend stop and the bias-device contact.

In accordance with an added feature of the invention, a magnitude of thelongitudinal bias is dependent upon a longitudinal position of the endstop within the body interior cavity.

In accordance with an additional feature of the invention, the biasdevice is disposed about at least a portion of the switching pistonbetween the end stop and the bias-device contact.

In accordance with yet another feature of the invention, thelongitudinal piston axis is disposed coincident with the longitudinaldevice axis.

In accordance with yet a further feature of the invention, the biasdevice imparts the longitudinal bias to retain the switching piston inthe switch-breaking piston position to create a normally open switchconfiguration.

In accordance with yet an added feature of the invention, the biasdevice imparts the longitudinal bias to retain the switching piston inthe switch-making piston position to create a normally closed switchconfiguration.

In accordance with yet an additional feature of the invention, adistance between the first longitudinal piston position and theswitch-breaking piston position is between approximately 25 μm andapproximately 750 μm, in particular, between approximately 75 andapproximately 200 μm,

In accordance with again another feature of the invention, a range offorce to switch between the switch-making state and the switch-breakingstate is between approximately 3 ounces and approximately 20 pounds, inparticular, between approximately 5 pounds to approximately 8 pounds.

In accordance with again a further feature of the invention, theelectrically-conductive contact is electrically insulated from the bodyand the switching piston.

In accordance with again an added feature of the invention, there isprovided a switch sub-assembly having the electrically-conductivecontact, a switch housing longitudinally fixedly and electricallyconductively connected to the body and at least partially surroundingthe electrically-conductive contact, a switch insulator electricallyinsulating the electrically-conductive contact from the switch housing,and a piston contact movably disposed in the housing and longitudinallyfixedly and electrically conductively connected to the switching piston.

In accordance with again an additional feature of the invention, theswitch insulator at least partially surrounds the piston contact, theelectrically-conductive contact at least partially surrounds the switchinsulator, and the switch housing at least partially surrounds theelectrically-conductive contact, the switch insulator, and the pistoncontact.

In accordance with still another feature of the invention, the switchinsulator at least partially surrounds the electrically-conductivecontact and the switch housing at least partially surrounds theelectrically-conductive contact, the switch insulator, and the pistoncontact.

In accordance with still a further feature of the invention, theswitching piston has a first circular-shaped exterior, the bias-devicecontact has a second circular-shaped exterior having a larger diameterthan the first circular-shaped exterior, the body interior cavity has afirst circular-shaped interior substantially equal to the secondcircular-shaped exterior, the second interior cavity has a secondcircular-shaped interior substantially equal to the firstcircular-shaped exterior, the bias device has a third circular-shapedexterior substantially equal to the first circular-shaped interior, andthe electrically-conductive contact has a fourth circular-shapedexterior smaller in diameter than the first circular-shaped interior.

In accordance with still an added feature of the invention, there isprovided an end stop defining a second interior cavity in which theswitching piston is movably disposed, the end stop being at least partlydisposed in the body interior cavity and wherein the switching piston.The end stop and the body form an assembly where the end stop isthreaded into the body interior cavity to longitudinally fix androtationally adjust the end stop within the body interior cavity or theend stop floats about the switching piston and within the body.

In accordance with still an additional feature of the invention, thereis provided an electric indication circuit electrically connected to theswitching piston and the electrically-conductive contact and having anindicator transmitting state-change information to a user signaling thata state change of the switching piston has occurred.

In accordance with a concomitant feature of the invention, there isprovided an end stop defining a second interior cavity in which theswitching piston is movably disposed, the end stop being at least partlydisposed in the body interior cavity and wherein the bias device is acompression spring compressed between the bias-device contact and theend stop around the switching piston to bias the switching piston in adirection away from the end stop .

Other features that are considered as characteristic for the inventionare set forth in the appended claims.

Although the invention is illustrated and described herein as embodiedin a force switch, it is, nevertheless, not intended to be limited tothe details shown because various modifications and structural changesmay be made therein without departing from the spirit of the inventionand within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however,together with additional objects and advantages thereof, will be bestunderstood from the following description of specific embodiments whenread in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of embodiments the present invention will be apparent fromthe following detailed description of the preferred embodiments thereof,which description should be considered in conjunction with theaccompanying drawings in which:

FIG. 1 is a perspective view from a side of an exemplary embodiment of aforce switch according to the invention.

FIG. 2 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 1 through a near half of the switch;

FIG. 3 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 1 through a near half of the switch;

FIG. 4 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 1 through a near half of the switch;

FIG. 5 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 1 through a near half of the switch;

FIG. 6 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 1 through approximately a longitudinal axisof the switch;

FIG. 7 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 1 through a far half of the switch;

FIG. 8 is an enlarged, longitudinally cross-sectional perspective viewfrom a side of the force switch of FIG. 6 with the switch in anun-actuated position;

FIG. 9 is an enlarged, longitudinally cross-sectional perspective viewfrom a side of the force switch of FIG. 6 with the switch in an actuatedposition;

FIG. 10 is a perspective view from a side of another exemplaryembodiment of a force switch according to the invention.

FIG. 11 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 10 through a near half of the switch;

FIG. 12 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 10 through a near half of the switch;

FIG. 13 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 10 through approximately a longitudinal axisof the switch;

FIG. 14 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 10 through a far half of the switch;

FIG. 15 is a longitudinally cross-sectional perspective view from a sideof the force switch of FIG. 10 through a far half of the switch;

FIG. 16 is an enlarged, longitudinally cross-sectional perspective viewfrom a side of the force switch of FIG. 13 with the switch in anun-actuated position; and

FIG. 17 is an enlarged, longitudinally cross-sectional perspective viewfrom a side of the force switch of FIG. 13 with the switch in anactuated position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Aspects of the invention are disclosed in the following description andrelated drawings directed to specific embodiments of the invention.Alternate embodiments may be devised without departing from the spiritor the scope of the invention. Additionally, well-known elements ofexemplary embodiments of the invention will not be described in detailor will be omitted so as not to obscure the relevant details of theinvention.

Before the present invention is disclosed and described, it is to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting. It must be noted that, as used in the specification and theappended claims, the singular forms “a,” “an,” and “the” include pluralreferences unless the context clearly dictates otherwise.

While the specification concludes with claims defining the features ofthe invention that are regarded as novel, it is believed that theinvention will be better understood from a consideration of thefollowing description in conjunction with the drawing figures, in whichlike reference numerals are carried forward. The figures of the drawingsare not drawn to scale.

Referring now to the figures of the drawings in detail and first,particularly to FIGS. 1 to 9 thereof, there is shown a first exemplaryembodiment of a force switch 1. FIGS. 10 to 17 illustrate a secondexemplary embodiment of the force switch 1. As will be described in moredetail below, the first exemplary embodiment represents a “normallyopen” switch configuration and the second exemplary embodimentrepresents a “normally closed” switch configuration. Where features ofthe switch 1 are similar in the two embodiments, for ease ofunderstanding, similar reference numerals will be used.

The force switch 1 can be incorporated into a device where force alongthe longitudinal axis of the device needs to be measured and an actionneeds to be taken when that force exceeds a given predetermined value.This force switch 1 can be used, for example, in a medical device, butis not limited to the exemplary embodiment of a medical device. As willbe described in further detail below, the force switch 1 can be usedwith a circular surgical stapling device such as is disclosed in U.S.Pat, No. 5,104,025 to Main

FIGS. 1 to 9 represent different portions of the force switch 1. FIG. 6provides an example view through the longitudinal axis 2 of the forceswitch 1 that allows one to see all parts of the switch 1. A contactpiston 10 provides a central part around which other parts of the switch1 may be explained. A nose piece or tip 20 is fastened to the distal end12 of the contact piston 10. The distal end 12 and an internal bore 22of the tip 20 are illustrated with straight lines in FIGS. 4 to 9,however, in a first exemplary embodiment, the distal end 12 can beprovided with external male threads and the bore 22 can be provided withinternal female threads. Alternatively, the tip 20 can be press-fit,glued, welded, or otherwise connected to the distal end 12 of thecontact piston 10. In the configuration shown in FIGS. 4 to 9, aproximal portion 24 of the internal bore 22 has a non-threaded flatportion for receiving therein the distal-most end of the piston 10 suchthat, when completely threaded into the bore 22, the proximal portion 24acts as a stop for further threading of the distal end 12 therein.

At the proximal end of the piston 10, a widening 14 is provided on theoutside surface of the piston 10 and an internal bore 16 is formed inthe interior thereof.

A hollow body tube 30 is disposed around at least a portion of thecontact piston 10. One exemplary embodiment of the interior of the tube30 includes a relatively narrower proximal bore 32 and a relativelywider distal bore 34 (although the opposite configuration is alsopossible). The bores 32, 34 surround a proximal portion of the piston 10that includes a central shaft 18 thereof and the widening 14. Theexterior shape of the widening 14 and the interior shape of the proximalbore 32 are substantially equal. Accordingly, in a circularconfiguration, the interior diameter of the proximal bore 32 issubstantially equal to the outer diameter of the widening 14. As usedherein, substantially equal means that there is only a sufficientclearance between the two parts to allow one to slide within the other.Thus, if a given first material requires a particular first spacingbetween the outer surface of the piston 10 and the inner surface of thebody tube 30 to permit the piston 10 to move therein, then that firstspacing exists between the two parts 10, 30, whereas, if a given secondmaterial requires a smaller (or larger) spacing between the outersurface of the piston 10 and the inner surface of the body tube 30 topermit the piston 10 to move therein, then that that second spacingexists between the two parts 10, 30.

There are two parts between the piston 10 and the body tube 30, anadjustable end cap 40 and a bias device 50. The exterior shape of theend cap 40 and the interior shape of the distal bore 34 aresubstantially equal. Accordingly, in a circular configuration, theinterior diameter of the distal bore 34 is substantially equal to theouter diameter of the end cap 40. Thus, when the end cap 40 is insertedinto the distal bore 34, the cap 40 substantially closes an interiorspace defined by the interior surfaces of the distal and proximal bores34, 32, the exterior surface of the central shaft 18, the distaltransverse surface of the widening 14, and the proximal end surface ofthe cap 40. The bias device 50 is disposed inside this interior space.The bias device 50 and the cap 40 act together with the widening 14 tobias the piston 10 in a given direction, in this case, in the proximaldirection. Force of the bias device 50 can be dependent upon theposition of the cap 40. For example, if the cap 40 is closer to thewidening 14, the bias device 50 can exert a first biasing force and ifthe cap 40 is further from the widening 14, the bias device 50 can exerta second biasing force. Depending upon the bias device 50 used, thefirst force can be greater than the second, or vice-versa. It isbeneficial, but not required, if the cap 40 is adjustable betweenvarious locations along the body tube 30. In such a configuration, thebias device 50 can be adjusted to a user-desired pre-bias.

One embodiment of the cap 40 and bias device 50 is shown in FIGS. 2 to9. The following description, however, will be directed to the view ofFIG. 8. In this embodiment, the distal bore 34 has a larger diameterthan the proximal bore 32. The end cap 40 has exterior threads 42 thatmate with non-illustrated internal female threads of the distal bore 34.In such a configuration, the cap 40 can be rotated into the distal bore34 along any longitudinal point within the distal bore 34. With theproximal bore 32 having a smaller diameter than the distal bore 34, thedistal endpoint 36 of proximal bore 32 forms a stop for insertion of thecap 40. The cap 40 is formed with an interior bore 44 having a shapesubstantially equal to the outer shape of the central shaft 18 of thepiston 10. Thus, while the cap 40 can be screwed into the distal bore 34such that longitudinal forces will not press the cap 40 out from thedistal bore 34, the central shaft 18 of the piston 10 can movelongitudinally freely within the bore 44 and with respect to the cap 40.

The bias device 50 is embodied, in this example, as a compression spring50. As such, when the spring 50 is placed around the central shaft 18 ofthe piston 10 up to the distal transverse surface of the widening 14,and when the threaded cap 40 is also placed around the central shaft 18and screwed at least partially within the distal bore 34, the spring 50can be compressed between two extremes defined by the longitudinalconnection distance that the cap 40 can traverse between being securelybut barely inside the distal bore 34 and fully inserted therein up tothe stop 36.

Because the piston 10 moves, it can form one contact of an electricalswitch for signaling a state of the piston 10. Another contact needs tobe provided that is electrically insulated from the piston 10. Thus, thepiston 10 needs to be associated with a switch sub-assembly so that theelectrical switch is in a first state when the piston 10 is in a firstlongitudinal position and in a second state when the piston 10 is in asecond longitudinal position (the first and second states being off/onor on/off). This switch sub-assembly is formed at a proximal end of thepiston 10 and the body tube 30 and, in the following text, is shown intwo exemplary embodiments. The first embodiment, the “normally open”switch has been mentioned as being related to FIGS. 1 to 9. The secondembodiment relates to FIGS. 10 to 17 and is a “normally closed” switch.

The normally open switch sub-assembly is explained with regard to FIGS.8 to 9. A switch bushing 60 has a distally projecting stub 62 that isinserted into the proximal end of the body tube 30. This stub 62 can beconnected to the body tube 30 in any number of ways (e.g., by bonding,welding, adhesive, press-fit, screw threads). The proximal end of theswitch bushing 60 is attached to a mounting body 70. In one embodiment,each of the piston 10, the tip 20, the body tube 30, the cap 40, theswitch bushing 60, and the mounting body 70 are electrically conductiveand provide a first electrical contact of the force switch 1. However,the tip 20 and cap 40 need not be conductive. To form a secondelectrical contact that, when put into electrical connection with thefirst contact, completes an electrical circuit (or interrupts anelectrical circuit as shown in FIGS. 10 to 17), an insulating body needsto be disposed between the second contact and the first contact needs tobe operatively moved into (or out of) contact with the second contact.

Various switch embodiments disclosed herein include parts that areelectrically conductive and actually form part of the electroniccircuit. The switch according to the present invention, however, is notlimited to embodiments where parts of the switch form the circuit. Analternative configuration can take advantage only of the mechanicalswitch-breaking aspects of the invention to have the movement of thepiston actuate a separate electrical switch adjacent the switch, e.g.,the piston. Such an external switch can be embodied as what is referredto in the art as a tact switch because such a switch is very small.Various microswitches can be used as well if there is sufficient roomfor such larger switches.

In the exemplary embodiment of FIGS. 1 to 9, the second electricalcontact is formed by a contact ring 80 and the insulating body is formedby an insulating stub 90. The part that connects the ring 80 and theinsulating stub 90 to the piston 10 is a T-shaped connecting bar 100.Each of the ring 80, the stub 90, and the bar 100 are nested in theirshape so that they can fit in an easy assembly into the switch bushingand the body tube 30. The insulating stub separates the contact ring 80from the connecting bar 100, which is in electrically conductive contactwith the piston 10 and the switch bushing 60.

More specifically, the internal bore 16 is shaped to receive a distalboss 102 of the connecting bar 100. The connection between the distalboss 102 and the internal bore 16 can be like any of the embodiments ofthe connection between the piston 10 and the tip 10. If the boss 102 hasan external male thread, for example, then the internal bore 16 has acorresponding female internal thread. Such an exemplary configurationmakes attachment of the connecting bar 100 and the piston 10 easy withregard to manufacturing costs and time.

The contact ring 80 has an internal bore 82 having a shape dimensionedto correspond substantially to the outer shape of a distal contactportion 92 of the insulating stub 90. This external outer shape of thedistal contact portion 92 can take any polygonal shape, such ascircular, ovular, rectangular, square, star, triangular, for example.Regardless of this outer shape, the shape of the internal bore of thecontact ring 80 corresponds thereto so that the contact ring 80 can beinserted thereon and fixed (whether by press-fit, adhesive, bonding,welding, or any other connection process) thereto so that control ofcontact between the ring 80 and any other portion of the first contactcan be made with high precision.

After the contact ring 80 is connected to the insulator stub 90, thecombined assembly can be connected to the connecting rod 100. Theexternal shape of an intermediate portion of the rod 100 is made tocorrespond to an internal shape of a bore 94 extending through theinsulator stub 90. Again, the outer shape of the intermediate portion ofthe rod 100 can take any polygonal shape, such as circular, ovular,rectangular, square, star, triangular, for example. Regardless of thisouter shape, the shape of the internal bore of the insulator stub 90corresponds thereto so that the insulator stub 90 can be insertedthereon and fixed (whether by press-fit, adhesive, bonding, welding, orany other connection process) thereto so that control of contact betweenthe ring 80, mounted to the stub 90, and any other portion of the firstcontact can be made with high precision.

With such a connection, the connecting rod 100 electrically contacts thepiston 10 (and, thereby, the tip 20, the body tube 30, the cap 40, theswitch bushing 60, and the mounting body 70). The outer shape/diameterof the contact ring 80 is dimensioned to be smaller than the innershape/diameter of the switch bushing 60 and insertion of the contactring 80 inside the switch bushing 60 creates a transverse gap 110therebetween. Thus, the contact ring 80 is electrically isolated fromthe switch bushing 60 on the outer side thereof by the transverse gap110 and is electrically isolated (insulated) from the connecting rod 100on the inner side thereof by being in direct contact with the outsidesurface of the insulator stub 90.

To make an electric circuit including the contact ring 80 and anyelectrically conducting part of the first contact (10, 20, 30, 40, 60,70), an electrical connection must be made at the contact ring 80. Oneexemplary embodiment for such a connection is illustrated in FIGS. 5 to9. Specifically, the connecting bar 100 is formed with the proximallongitudinal bore 103 extending from the proximal transverse exteriorsurface 104 up to and including at least a part of the intermediateportion the connecting rod 100 that is located at a longitudinalposition where the contact ring 80 is disposed. A further transversebore 106 is formed to connect the longitudinal bore 103 with an interiorsurface of the contact ring 80. In such a configuration, an insulatedwire 206 can be threaded through the longitudinal 103 and transverse 104bores and fastened (e.g., by welding) to the interior surface of thecontact ring 80. For ease of such a connection, the contact ring 80 canbe formed with a depression (or a series of depressions) on the insidesurface for receiving the electrical portion of the wire while theinsulating portion of the wire remains in contact with the entirety ofthe longitudinal 103 and transverse 104 bores of the connecting rod 100.

Such an electrical connection is, for example diagrammatically shown inFIG. 7, where circuitry 200 is disposed between the contact ring 80 andthe mounting body 70. This exemplary circuitry includes a power source202 and a contact indicator 204 (i.e., an LED) that lights the LED whenthe electrical circuit is completed. If the mounting body 70 and theinsulated wire 206 are each connected to the circuitry 200 (as shown inFIG. 7), then, when electrical contact occurs between the contact ring80 and any part of the first contact (10, 20, 30, 40, 60, 70), the LED204 will illuminate.

With the above exemplary configuration set forth, the functioning of theswitch 1 between the first and second states can be described withregard to a comparison between FIGS. 8 and 9. The piston 10 islongitudinally fixed to the tip 20 and to the connecting rod 100.Further, the insulator stub 90 and the contact ring 80 arelongitudinally fixed to the exterior of the connecting rod 100. Thepiston 10 is slidably disposed inside the bore 44 of the cap 40 at thedistal end and is slidably disposed inside the proximal bore 32 of thetube body 30. Thus, the entire piston sub-assembly (10, 20, 80, 90, 100)can move in a longitudinal direction because a longitudinal gap 112exists between the distal transverse surface of the contact ring 80 anda proximal end surface 64 of the stub 62 of the switch bushing 60. It isthis gap 112 that forms the space over which the force switch 1 canfunction.

The bias device (e.g., compression spring) 50 disposed between theadjustable cap 40 and the distal transverse surface of the widening 14imparts a proximally directed force against the piston 10 when the cap40 is adjusted to compress the spring 50. This force, referred to hereinas a pre-tension, keeps the contact ring 80 at a distance from theelectrically conductive stub 62 of the switch bushing 60—which isdefined as the longitudinal gap 112. Without any external force impartedon the force switch 1, the pre-tension will always keep the contact ring80 at this position and electrical contact between the first contact andthe contact ring 80 will not occur. A distally directed external force Fimparted upon the tip 20 could alter this situation. See FIG. 9. If theforce F is not as great as the pre-tension force imparted by the spring50, then the spring will not compress any further than it has alreadybeen compressed by the adjustable cap 40. However, if the force F isgreater than the pre-tension force imparted by the spring 50, then thespring will compress and the tip 20 along with the remainder of thepiston sub-assembly—the piston 10, the connecting rod 100, theinsulating stub 90, and the contact ring 80—will move in a distallongitudinal direction. The distal longitudinal direction is limited bythe proximal end surface 64 of the stub 62 of the switch bushing 60because contact between the end surface 64 and the distal side of thecontact ring 80 completely prevents further movement of the tip 20. Thisconfiguration, therefore, provides an electrical switch that has anadjustable longitudinal pre-tension force that must be overcome beforethe switch 1 can actuate and complete the electrical circuit that is“open” until the contact ring 80 touches the switch bushing 60. FIG. 9shows the piston sub-assembly (10, 20, 80, 90, 100) in the actuateddistal position and FIG. 8 shows the piston sub-assembly in theun-actuated proximal position

One exemplary process for assembly of the force switch 1 of FIGS. 1 to9, has the spring 50 inserted over the central shaft 16 of the piston10. The cap 40 is also screwed into the proximal bore 34 of the bodytube 30. The piston-spring sub-assembly is, then inserted through theinterior bore 44 of the cap 40 and the tip 20 is fastened (e.g.,screwed) onto the distal end 12 of the piston 10. This forms a pistonsub-assembly.

The insulating stub 90 is attached to the intermediate portion of theconnecting bar 100 by being placed, first, over the distal boss 102 and,second, over the intermediate portion. Similarly, the contact ring 80 isattached to the insulating stub 90 by being placed thereover. The ring80 is longitudinally connected to the insulating stub 90 and the stub 90is longitudinally connected to the intermediate portion of theconnecting bar 100. The insulated wire 206 is passed through the bore ofthe mounting body 70 and through both the longitudinal 103 andtransverse 106 bores of the connecting rod 100 and electricallyconnected to the interior surface of the contact ring 80 withoutelectrically connecting the wire 206 to any portion of the mounting body70 or the connecting bar 100. This connection forms a switchsub-assembly that is ready to be connected to the piston sub-assembly.

Either or both of the distal boss 102 of the connecting bar 100 or thestub 62 of the switch bushing 60 can have threads for connecting theboss 102 to the piston 10 and/or the stub 62 to the body tube 30. Assuch, the entire switch sub-assembly can be connected (both physicallyand electrically) to the piston sub-assembly. With these twosub-assemblies connected together, only the mounting body 70 needs to beconnected to the proximal end of the switch bushing 60. Such aconnection can take any form, for example, the connection can be a weldor a mated set of screw threads.

FIGS. 10 to 17 illustrate a second exemplary embodiment of the forceswitch 1 having a “normally closed” switch configuration.

FIGS. 10 to 17 illustrate different portions of the force switch 1. FIG.14 provides an example view approximately through the longitudinal axis2 of the force switch 1 that allows visualization of all parts of theswitch 1. The contact piston 10 provides a central part around whichother parts of the switch 1 may be explained. The tip 20 is fastened tothe distal end 12 of the contact piston 10. The distal end 12 and theinternal bore 22 of the tip 20 are illustrated with straight lines inFIGS. 13 to 15 and 17, however, in the exemplary embodiment, the distalend 12 can be provided with external male threads and the bore 22 can beprovided with internal female threads. Alternatively, the tip 20 can bepress-fit, glued, welded, or otherwise connected to the distal end 12 ofthe contact piston 10. In the configuration shown in FIGS. 13 to 15 and17, the proximal portion 24 of the internal bore 22 has the non-threadedflat portion for receiving therein the distal-most end of the piston 10such that, when completely threaded into the bore 22, the proximalportion 24 acts as a stop for further threading of the distal end 12therein.

The piston 10 has a proximal end at which the widening 14 is provided toextend radially the outside surface of the piston 10. The internal bore16 is formed in the interior of the piston 10 at the proximal end.

As shown in the enlarged view of FIG. 16, a hollow body tube 120 isdisposed around at least a portion of the contact piston 10. As comparedto the first embodiment of the body tube 30, the interior of this tube120 has a constant diameter bore 122. The bore 122 has a shapesubstantially equal to an exterior shape of the widening 14 andsurrounds the central shaft 18 of the piston 10. Accordingly, in acircular configuration, the interior diameter of the bore 122 issubstantially equal to the outer diameter of the widening 14.

There are two parts of the force switch 1 disposed between the piston 10and the body tube 120: a spring stop puck 130 and a bias device 50. Theexterior shape of the spring stop puck 130 and the interior shape of thebore 122 are substantially equal. Accordingly, in a circularconfiguration, the interior diameter of the bore 122 is substantiallyequal to the outer diameter of the spring stop puck 130 so that thespring stop puck 130 slides within the bore 122 substantially withoutplay but also without substantial friction. This spring stop puck 130differs from the end cap 40 in that it floats entirely separate withinthe body tube 120. More specifically, as the tip 20 is threaded onto thedistal end 12 of the piston 10, the proximal transverse surface pushesagainst but is not fixed to the distal transverse surface of the puck130. In such a configuration, it would, at first glance, seem toindicate that the compression spring 50 could only be set to one givencompression value because the puck 130 has a fixed longitudinal length.This would be correct except a set of pucks 130 are provided, eachhaving different longitudinal lengths. Therefore, the pre-tensioning ofthe spring 50 is adjusted by selecting one of the set of pucks 130.Also, it is not necessary to thread the tip 20 entirely onto the distalend 12 of the piston 10 as shown in FIG. 13, for example. Thus, if thetip 20 is not entirely threaded on the piston 10, user-desiredpre-tensioning of the bias device 50 occurs by providing a specificallysized puck 130 and threading the tip 20 onto the piston 10 at apredefined distance. Alternatively, the puck 130 can solely determinethe pre-tension if the tip 20 is entirely threaded onto to the piston10. One embodiment of the stop puck 130 and bias device 50 is shown inFIGS. 10 to 17. The following description, however, is directed to theview of FIG. 13. The stop puck 130 is formed with an internal bore 132having a shape substantially equal to the outer shape of the piston 10so that the piston 10 can traverse through the puck 130 withouthindrance.

When the spring stop puck 130 is within the bore 122, the stop puck 130substantially closes an interior space defined by the interior surfacesof the bore 122, the exterior surface of the central shaft 18, thedistal transverse surface of the widening 14, and the proximaltransverse surface of the puck 130. The bias device 50 is disposedinside this interior space. The bias device 50 and the stop puck 130 acttogether with the widening 14 to bias the piston 10 in a givendirection, in this case, in the proximal direction. Force of the biasdevice 50 is dependent upon the longitudinal length of the stop puck130.

The bias device 50 is embodied, in this example, as a compression spring50. As such, when the spring 50 is placed around the central shaft 18 ofthe piston 10 up to the distal transverse surface of the widening 14,and when the stop puck 130 is also around the central shaft 18 and thetip 20 is attached to the piston 10, the spring 50 is compressed orpre-tensioned therebetween.

Because the piston 10 moves, it can form one contact of an electricalswitch for signaling a state of the force switch 1. Another contactneeds to be provided that is electrically insulated from the piston 10.Thus, the piston 10 needs to be associated with a switch sub-assembly sothat the electrical force switch 1 is in a first state when the piston10 is in a first longitudinal position and in a second state when thepiston 10 is in a second longitudinal position (the first and secondstates being off/on or on/off). This switch sub-assembly is formed at aproximal end of the piston 10 and the body tube 120 and, in thefollowing text, applies to the second exemplary “normally closed”embodiment.

The switch bushing 60 has a distally projecting stub 62 that is insertedinto the proximal end of the body tube 120. This stub 62 can beconnected to the body tube 120 in any number of ways (e.g., by bonding,welding, adhesive, press-fit, screw threads). The proximal end of theswitch bushing 60 is attached to a mounting body 70. In one embodiment,each of the piston 10, the tip 20, the body tube 120, the stop puck 130,the switch bushing 60, and the mounting body 70 are electricallyconductive and provide a first electrical contact of the force switch 1,However, the tip 20 and stop puck 130 need not be electricallyconductive. To form a second electrical contact that, when put intoelectrical connection with the first contact, interrupts an electricalcircuit as shown in FIGS. 10 to 17, an insulating body needs to bedisposed between the second contact and the first contact needs to beoperatively moved out of contact with the second contact.

In the exemplary embodiment of FIGS. 10 to 17, the second electricalcontact is formed by a contact pin 140 and the insulating body is formedby an insulating bushing 150. The part that connects the insulatingbushing 150 and the contact pin 140 to the piston 10 is a T-shaped,electrically conductive, contact screw 160. The insulating bushing 150and the contact pin 140 are nested in their shape so that they can fitin an easy assembly into the switch bushing 60 and the mounting body 70.The insulating bushing 150 physically and electrically separates thecontact pin 140 from the mounting body 70 and the switch bushing 60,which is in electrically conductive contact with at least the piston 10and the switch bushing 60.

More specifically, the internal bore 16 is shaped to receive a distalboss 162 of the contact screw 160. The connection between the distalboss 162 and the internal bore 16 can be like any of the embodiments ofthe connection between the piston 10 and the tip 10. If the boss 162 hasan external male thread, for example, then the internal bore 16 has acorresponding female internal thread. Such an exemplary configurationmakes attachment of the contact screw 160 and the piston 10 easy withregard to manufacturing costs and time. A transverse end surface 164 ofthe contact screw 160 also provides a stop for indicating completeinsertion of the distal boss 162 inside the internal bore 16 of thepiston 10.

The insulating bushing 150 has an internal bore 152 having a shapedimensioned to correspond substantially to the outer shape of a proximalcontact portion 142 of the contact pin 140. This external outer shape ofthe proximal contact portion 142 can take any polygonal shape, such ascircular, ovular, rectangular, square, star, triangular, for example.Regardless of this outer shape, the shape of the internal bore 152 ofthe insulating bushing 150 corresponds thereto so that the insulatingbushing 150 can be inserted thereon and fixed thereto (whether bypress-fit, adhesive, bonding, welding, or any other connection process)so that control of contact between the contact pin 140 and any otherportion of the first contact can be made with high precision.

After the insulating bushing 150 is connected to the contact pin 140,the combined insulating sub-assembly can be connected to the mountingbody 70. The external shape of a proximal portion of the insulatingbushing 150 is made to correspond to an internal shape of an internalbore 72 extending through the mounting body 70. Again, the outer shapeof the proximal portion of the insulating bushing 150 can take anypolygonal shape, such as circular, ovular, rectangular, square, star,triangular, for example. Regardless of this outer shape, the shape ofthe internal bore of the mounting body 70 corresponds thereto so thatthe insulating bushing 150 can be inserted thereon and fixed thereto(whether by press-fit, adhesive, bonding, welding, or any otherconnection process) so that control of contact between the contact pin140 (mounted in the insulating bushing 150 and the mounting body 70) andany other portion of the first contact can be made with high precision.

With such a connection, the contact screw 160 electrically contacts thepiston 10 (and, thereby, the body tube 120, the switch bushing 60, andthe mounting body 70, and possibly even the tip 20 and the stop puck 130if desired). The outer shape/diameter of a distal transverse widening144 of the contact pin 140 is dimensioned to be smaller than the innershape/diameter of the switch bushing 60 and insertion of the contact pin140 inside the switch bushing 60 creates a transverse gap 110therebetween. Thus, the transverse gap 110 electrically isolates thedistal widening 144 of the contact pin 140 from the inside of the switchbushing 60, and the proximal contact portion 142 of the contact pin 140is electrically isolated (insulated) from the mounting body 70 and theswitch bushing 60 on the outer side thereof by being in direct contactwith the interior bore 152 of the insulating bushing 150.

To make an electric circuit between the contact pin 140 and anyelectrically conducting part of the first contact (e.g., 10, 20, 60, 70,120, 130), an electrical connection must be made at the contact pin 140.One exemplary embodiment for such a connection is illustrated in FIGS.11 to 17. Specifically, the contact screw 160 is formed with a proximaltransverse widening 166 extending radially from the intermediate portionthereof and defines a proximal transverse surface 168. The bias device50 biases the piston 10 and, thereby, the contact screw 160 in aproximal direction to electrically conductively contact the distaltransverse surface 148 of the contact pin 140 to the proximal transversesurface 168 of the contact screw 160. Because such contact needs to onlybe made between these two surfaces to complete an electrical circuit ofthe switch sub-assembly, the outer shape/diameter of the proximalwidening 166 of the contact screw 160 can be any size or shape thatslides within the interior bore 66 of the switch bearing 60.

The other electrical contact of the contact pin 140 resides on theproximal side of the contact pin 140. In one exemplary embodiment, alongitudinal bore 146 is formed from the proximal transverse surface ofthe contact pin 140 inward and receives therein an insulated wire 206.The conductor of this wire 206 can be fastened (e.g., by welding) to theinterior surface of the longitudinal bore 146. Such an electricalconnection is, for example diagrammatically shown in FIG. 7. In such anexemplary configuration, the power source 202 supplies power to thecontact indicator 204 (LED) and lights the LED when the electricalcircuit is completed, which will always be the case in this normallyclosed configuration of the force switch 1. Conversely, when electricalcontact between the first contact and the contact pin 140 is removed,the LED 104 will turn off Of course, the indicator need not be visual(e.g., the LED 104). It can also be audible (e.g., speaker with sound)or tactile (e.g., vibration), or any combination thereof.

It is also possible to provide circuitry 300 between the contact pin 140and the mounting body 70 that lights the LED 204 only when theelectrical circuit is opened (i.e., not completed). Any logic circuitrycan be used to control the LED 204 based upon the two states of theforce switch 1 shown in FIGS. 10 to 17. For example, the logic 300including a NOR gate and an AND gate can be connected to the forceswitch 1 circuit as shown in FIG. 13. In such a configuration, When theswitch 1 is in its normally closed state, the LED is off and whencontact is broken, as shown in FIG. 17, the LED will illuminate.

With the above exemplary configuration set forth, the functioning of theswitch 1 between the first and second states can be described withregard to a comparison between FIGS. 16 and 17.

As set forth above, the contact pin 140 is longitudinally secured withinthe insulating bushing 150 and the insulating bushing 150 islongitudinally secured within at least one of the switch bearing 60 andthe mounting body 70. The body tube 120 is longitudinally secured to thedistal end of the switch bearing 60. The stop puck 130 is disposed,freely longitudinally, between the spring 50 and the tip 20. The piston10 is longitudinally fixed to the tip 20 and to the contact screw 160and this piston sub-assembly slides within the body 120 biased in theproximal direction by the spring 50. Accordingly, the entire pistonsub-assembly (10, 20, 130, 160) can move in a distal longitudinaldirection to compress the spring 50 inside the body tube 120 and thiscompression distance forms a space 134 (see FIG. 17) over which theforce switch 1 functions as a switch.

The bias device (e.g., compression spring) 50 disposed between the puck130 and the distal transverse surface of the widening 14 imparts aproximally directed force against the piston 10 when the puck 130compresses the spring 50. This force, referred to herein as apre-tension, keeps the contact screw 160 against the electricallyconductive distal transverse surface of the contact pin 140. Without anyexternal force imparted on the force switch 1, the pre-tension willalways keep the contact pin 140 at this position and electrical contactbetween the first contact and the contact pin 140 will remain. Adistally directed external force F imparted upon the tip 20 could alterthis situation. See FIG. 17. If the force F is not as great as thepre-tension force imparted by the spring 50, then the spring 50 will notcompress any further than it has already been compressed by the puck130. However, if the force F is greater than the pre-tension forceimparted to the piston 10 by the spring 50, then the spring 50 willcompress further and the tip 20, along with the remainder of the pistonsub-assembly (10, 130, 160) will move in a distal longitudinaldirection. The distal longitudinal direction is limited by the greatestcompression distance of the spring 50, which, in most applications ofthe force switch 1, will not occur. This configuration, therefore,provides an electrical switch that has an adjustable longitudinalpre-tension force that must be overcome before the switch 1 can actuateand complete the electrical circuit that is “closed” until the contactscrew 160 no longer touches the contact pin 140. The switching distanceof the force switch 1 of FIGS. 10 to 17 is defined by the longitudinalgap 112 existing between the proximal transverse surface of the stub 62and the distal transverse surface of the widening 166. FIGS. 17 and 19show the piston sub-assembly (10, 130, 160) in the actuated distalposition and FIG. 16 shows the piston sub-assembly in the un-actuatedproximal position.

One exemplary process for assembly of the force switch 1 of FIGS. 10 to17, the distal end of the switch bushing 60 having the projecting stub62 is fastened longitudinally to the proximal end of the body tube 120.The piston 10 inserted inside the body tube 120 and the spring 50inserted over the central shaft 16 of the piston 10 inside the body tube120. The puck 130 is placed over the distal end 12 of the piston 10 andthe tip 20 is fully or partially screwed onto the exterior threads ofthe distal end 12 of the piston 10. At this point, if the tip is fullyscrewed onto the piston 10, the piston 10 will impart the pre-tensionforce onto the stub 62 of the switch bushing. To avoid this force, thetip 20 can be only partially screwed onto the distal end 12 of thepiston 10. The contact screw 160 is, then, screwed into the internalbore 16 of the piston 10 at the proximal end thereof to capture the stub62 between the widening 14 of the piston 10 and the widening 166 of thecontact screw 160. This forms a piston-spring sub-assembly.

The mounting body 70 is longitudinally fixedly connected to the contactpin 140 with the insulating bushing 150 therebetween. Because of thenested shapes of these parts, the order of the connection is limitedonly by the costs and time for manufacturing the connections.Alternatively, the insulating bushing 150 and the contact pin 140 can beplaced inside the distal end of the mounting body 70, but, in such acase, these two parts could move longitudinally if the distal end of theforce switch 1 is tilted downward. This forms a contact pinsub-assembly.

The piston-spring and contact pin sub-assemblies are connected togetherby fastening, longitudinally, the mounting body 70 to the switch bushing60. If the tip 20 is fully screwed onto the piston 10, then thefastening will have to overcome the pre-bias force of the spring 50. If,however, the tip 20 is minimally screwed onto the piston 10 such that nopre-bias exists in the spring 50, then, after all longitudinal fasteninghas occurred, the tip 20 can be fully screwed onto the distal end 12 ofthe piston 10 to place the spring 50 in the pre-tensioned state. Theconductor of the insulated wire 206 is attached in the longitudinal bore146 of the contact pin 140 to complete the circuit 300.

In each case of the normally open and normally closed configurations,the longitudinal gap 112 has a length of between approximately 25 μm(0.001″) and approximately 750 μm (0.030″), or in a shorter rangebetween approximately 75 μm (0.003″) and approximately 200 μm (0.008″).

The conductive parts of the force switch 1 can be of stainless steel,copper, nickel-plated copper, nickel-plated brass, for example. Wherethe conductor of the insulated wire 206 needs to be soldered, each ofthese materials will be sufficient.

The range of force that the force switch 1 applicable for switchingbetween the two states can be between approximately 3 ounces toapproximately 20 pounds, or a shorter range of approximately 5 pounds toapproximately 8 pounds.

With regard to the mechanics of selecting the spring 50, the desiredpre-tension force is selected to be within or at the mid-range of therange of a given spring 50. In other words, the change in state of theforce switch will occur not close to a maximum of the spectrum of thespring 50 pre-tension but, instead, somewhere in the middle of thespectrum.

The circuitry described above only provides a binary output—whether ornot the force on the external object that is transmitted through theforce switch 1 is greater or less than the pre-tensioning. If the forceswitch is provided with a strain gauge, also referred to as a load cell,then a continuous force output can be displayed to the user in which,for example, a row of LEDs gradually light up dependent upon the amountof force or an LCD or LED numerical field increments numerical valuescorresponding to the amount of force imparted through the force switch1.

The force switch 1 above will now be described with respect to use in anintraluminal anastomotic circular stapler as depicted, for example, inU.S. Pat. No. 5,104,025 to Main et al. (“Main”), and assigned to EthiconEndo-Surgery, Inc. This reference is hereby incorporated herein in itsentirety. As can be seen most clearly in the exploded view of FIG. 7 inMain, a trocar shaft 22 has a distal indentation 21, some recesses 28for aligning the trocar shaft 22 to serrations 29 in the anvil and,thereby, align the staples with the anvils 34. A trocar tip 26 iscapable of puncturing through tissue when pressure is applied thereto.FIGS. 3 to 6 in Main show how the circular stapler 10 functions to jointwo pieces of tissue together. As the anvil 30 is moved closer to thehead 20, tissue is compressed therebetween, as particularly shown inFIGS. 5 and 6. If this tissue is overcompressed, this surgical staplingprocedure might not succeed. The interposed tissue can be subject to arange of acceptable compressing force during surgery. This range isknown and is dependent upon the tissue being stapled. The stapler shownin Main cannot indicate to the user any level of compressive force beingimparted upon the tissue prior to stapling. However, if the force switch1 described herein is substituted for the trocar shaft 22, then thestapler 10 will be capable of showing the user when the compressiveforce (acting along the longitudinal axis 2 of the force switch 1) hasexceeded the pre-tension of the switch 1. This pre-tension can beselected by the user to have a value within the range of acceptabletissue compressive force.

FIGS. 1 and 10 of the present application show a tip 20 having a pointeddistal end that can function within at least the CDH surgical staplermanufactured and sold by Ethicon Endo-Surgery, Inc. The proximal end ofthe trocar shaft 22 in Main requires a male threaded screw forattachment to the head 20. Other circular staplers require an opposingtang embodiment that is shown in FIGS. 1 and 10 of the presentapplication. Thus, the mounting body 70 can be in the form illustratedin FIGS. 1 to 17 or in the form shown in FIG. 7 in Main. The tip 20 andmounting body 70 can be customized to fit into any kind of similarsurgical device.

The foregoing description and accompanying drawings illustrate theprinciples, preferred embodiments and modes of operation of theinvention. However, the invention should not be construed as beinglimited to the particular embodiments discussed above. Additionalvariations of the embodiments discussed above will be appreciated bythose skilled in the art.

Therefore, the above-described embodiments should be regarded asillustrative rather than restrictive. Accordingly, it should beappreciated that variations to those embodiments can be made by thoseskilled in the art without departing from the scope of the invention asdefined by the following claims.

1. A method of creating a mechanical force switch to be disposed along alongitudinal axis of a medical device, comprising: providing a hollowbody defining a body interior cavity with a longitudinal device axis;movably disposing a switching piston along the longitudinal device axisin the body interior cavity to define: a switch-making piston positionat a first longitudinal piston position with respect to the body; and aswitch-breaking piston position at a second longitudinal piston positionwith respect to the body that is different from the first longitudinalpiston position, the switching piston having: a longitudinal piston axisdisposed parallel to the longitudinal device axis; and a bias-devicecontact; coupling an electrically-conductive contact to the switchingpiston such that the electrically-conductive contact is moveable betweenthe two piston positions to define a switch-making state, when theswitching piston is in the switch-making piston position, and aswitch-breaking state, when the switching piston is in theswitch-breaking piston position; and imparting a variable longitudinalbias to the switching piston at the bias-device contact with a biasdevice to retain the switching piston in one of two positions selectedfrom the switch-making piston position and the switch-breaking pistonposition until an external force imparted to the switching pistonexceeds the longitudinal bias thereby forcing the switching piston tomove to the other of the two piston positions, thereby providing theswitching piston with a variable longitudinal pre-tension force thatmust be overcome before the force switch can actuate electrically. 2.The method according to claim 1, which further comprises defining asecond interior cavity by an end stop in which the switching piston ismovably disposed, the end stop being at least partly disposed in thebody interior cavity.
 3. The method according to claim 2, wherein thebias device is disposed about at least a portion of the switching pistonbetween the end stop and the bias-device contact.
 4. The methodaccording to claim 3, wherein the magnitude of the longitudinal bias isdependent upon a longitudinal position of the end stop within the bodyinterior cavity.
 5. The method according to claim 1, wherein thelongitudinal piston axis is disposed coincident with the longitudinaldevice axis.
 6. The method according to claim 1, wherein the bias deviceimparts the longitudinal bias to retain the switching piston in theswitch-breaking piston position to create a normally open switchconfiguration.
 7. The method according to claim 1, wherein the biasdevice imparts the longitudinal bias to retain the switching piston inthe switch-making piston position to create a normally closed switchconfiguration.
 8. The method according to claim 1, wherein a distancebetween the first longitudinal piston position and the switch-breakingpiston position is between approximately 25 μm and approximately 750 μm.9. The method according to claim 1, wherein a distance between the firstlongitudinal piston position and the switch-breaking piston position isbetween approximately 75 μm and approximately 200 μm.
 10. The methodaccording to claim 1, wherein a range of force to switch between theswitch-making state and the switch-breaking state is betweenapproximately 3 ounces and approximately 20 pounds.
 11. The methodaccording to claim 1, wherein a range of force to switch between theswitch-making state and the switch-breaking state is betweenapproximately 5 pounds to approximately 8 pounds.
 12. The methodaccording to claim 1, which further comprises electrically insulatingthe electrically-conductive contact from the body and the switchingpiston.
 13. The method according to claim 1, which further comprises:forming a switch sub-assembly having: the electrically-conductivecontact; a switch housing electrically conductively connected to thebody and at least partially surrounding the electrically-conductivecontact; a switch insulator electrically insulating theelectrically-conductive contact from the switch housing; and a pistoncontact movably disposed in the housing and electrically conductivelyconnected to the switching piston.
 14. The method according to claim 13,wherein: the switch insulator at least partially surrounds the pistoncontact; the electrically-conductive contact at least partiallysurrounds the switch insulator; and the switch housing at leastpartially surrounds the electrically-conductive contact, the switchinsulator, and the piston contact.
 15. The method according to claim 13,wherein: the switch insulator at least partially surrounds theelectrically-conductive contact; and the switch housing at leastpartially surrounds the electrically-conductive contact, the switchinsulator, and the piston contact.
 16. The method according to claim 2,wherein: the switching piston has a first circular-shaped exterior; thebias-device contact has a second circular-shaped exterior having alarger diameter than the first circular-shaped exterior; the bodyinterior cavity has a first circular-shaped interior substantially equalto the second circular-shaped exterior; the second interior cavity has asecond circular-shaped interior substantially equal to the firstcircular-shaped exterior; the bias device has a third circular-shapedexterior substantially equal to the first circular-shaped interior; andthe electrically-conductive contact has a fourth circular-shapedexterior smaller in diameter than the first circular-shaped interior.17. The method according to claim 1, further comprising: defining asecond interior cavity by an end stop in which the switching piston ismovably disposed, the end stop being at least partly disposed in thebody interior cavity and wherein the switching piston, the end stop andthe body form an assembly selected from the group comprised of: the endstop being threaded into the body interior cavity to longitudinally fixand rotationally adjust the end stop within the body interior cavity;and the end stop floating about the switching piston and within thebody.
 18. The method according to claim 1, which further compriseselectrically coupling an electric indication circuit to the switchingpiston and the electrically-conductive contact, the electric indicationcircuit having an indicator transmitting state-change information to auser signaling that a state change of the switching piston has occurred.19. The method according to claim 1, further comprising defining asecond interior cavity by an end stop in which the switching piston ismovably disposed, the end stop being at least partly disposed in thebody interior cavity and wherein the bias device is a compression springcompressed between the bias-device contact and the end stop around theswitching piston to bias the switching piston in a direction away fromthe end stop.